High-loading adsorbent/organic matrix composites

ABSTRACT

Crystalline molecular sieves which comprise mostly single and/or twinned crystal particles can be loaded into organic matrices in comparatively high amounts with less viscosity buildup than molecular sieves conventionally used for such desiccant applications. Desiccant/organic matrix compositions made with the single and/or twinned crystal zeolites exhibit improved rheological and adsorption characteristics in comparison to conventional systems. The compositions are especially useful in insulated glass window spacer applications.

This is a continuation of application Ser. No. 08/451,606, filed May 26,1995 now abandoned.

BACKGROUND OF THE INVENTION

Inorganic adsorbent materials, such as molecular sieves, zeolites, etc.,have long been used to remove constituents from (gaseous and/or liquid)fluids. Zeolites such as zeolites A and X are widely used in desiccatingand gas treatment applications.

In many instances, the adsorbent material is used in the form of a freeflowing particulate (e.g. beads) which is allowed to contact the fluidto be treated. In other instances, the adsorbent may be embedded in arigid monolithic structure such as a honeycomb. For many applications,these forms of the adsorbent cannot be used practically. For example, inthe window spacer structures disclosed in U.S. Pat. Nos. 5,177,916 and5,255,481, the adsorbent material is loaded into an organic matrix whichis then adhered to the spacer.

In many adsorbent/organic matrix composites, the adsorbent is typicallyincorporated into the organic matrix by mechanical mixing while theorganic matrix material is in a very soft or molten state. It isgenerally desirable to incorporate as much of the adsorbent as possibleper unit of organic matrix so as to enhance the adsorption performanceof the adsorbent/organic matrix composite as well as to reduce the costof the composite in situations where the organic material is moreexpensive than the adsorbent. Unfortunately, the amount of adsorbentwhich can be loaded into the composite is often limited by viscositybuildup which occurs during incorporation of the adsorbent as well as bya loss of workability and/or physical integrity in the resultingcomposite where the composite is applied to a substrate as in the abovementioned window spacer structures.

The viscosity buildup associated with commercial adsorbent molecularsieves is generally assumed to be constant and unalterable. While itmight be possible to increase the adsorbent loading by developingspecialized organic matrix materials or additives therefor, thesealternatives likely would be expensive. Thus, there is a need foradsorbent/organic matrix compositions having high adsorbent loading forthe organic matrix material selected, yet with minimal sacrifice ofworkability and/or physical integrity in the resulting composite.

SUMMARY OF THE INVENTION

The invention overcomes the disadvantages of known inorganicadsorbent/organic matrix composites by the use of adsorbent molecularsieve particles wherein at least a substantial portion of particles aresingle (and/or twinned) crystal particles. The use of single crystaladsorbent particles allows higher adsorbent loading to be achieved withthe resulting improved adsorption performance, but without excessiveviscosity buildup in mixing and without loss of workability and/orphysical integrity in the resulting composite.

In one aspect, the invention encompasses compositions comprisingmolecular sieve particles in an organic matrix wherein at least aportion of the molecular sieve particles are in the form of singleand/or twinned crystals. The molecular sieve particles are preferablyzeolites. Preferably, the organic matrix is a thermoplastic organicmaterial such as a so-called "hot melt" adhesive. The adsorbent/organicmatrix compositions are preferably suitable for use in insulating glasswindow spacer applications.

These and other aspects of the invention will be described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plot of viscosity vs. adsorbent loading for variousadsorbent/organic matrix composites.

DETAILED DESCRIPTION OF THE INVENTION

The invention encompasses the concept that the loading of molecularsieve adsorbents (especially zeolite desiccants) in an organic matrixcan be increased from loadings possible with commercial molecular sievesconventionally used for desiccant applications. This result is madepossible by the use of molecular sieves which contain a substantialamount of single and/or twinned crystal particles compared to molecularsieves normally used in desiccant applications.

The nature of most crystalline molecular sieve particles which arecommercially available for desiccant applications is that a largeportion (if not all) of the particles are polycrystalline particleswherein the crystals are intergrown. In comparison, the crystallinemolecular sieves used in the invention comprise a substantial portion ofsingle crystal and/or twinned crystal particles. Preferably, thecrystalline molecular sieve component used in the invention compositionscontains at least about 50% of single and/or twinned crystal particles.Most preferably, the crystalline molecular sieve component used in theinvention compositions consists essentially of single and/or twinnedcrystal particles.

While the degree of single and/or twinned crystal character of molecularsieve particles can be determined by microscopic techniques, a "wetting"test has been developed to distinguish crystalline molecular sieveswhich have suitable single and/or twinned crystal morphology. In thewetting test, a 10 gram sample of crystalline molecular sieve powder(activated at 315° C. for 2 hours) is placed into a ceramic mortar.Water is then added dropwise to the powder while mixing the powder witha pestle. The water addition and mixing is continued until a ratherdistinct thixotropic endpoint is reached at which a slight shear appliedto the damp powder (achieved by slowly turning the pestle on the surfaceof the powder) results in fluid flow of the mixture. The wetting testvalue is the mass of water (grams) required to reach the thixotropicendpoint. Wetting test values less than about 8.5 correspond tomolecular sieves having mostly single and/or twinned crystal particleswhereas values of 9 or more correspond to molecular sieves containingmostly intergrown polycrystalline particles.

The amount of the molecular sieve adsorbent incorporated into theorganic matrix can vary depending on the desired desiccating capacity,the rheological properties of the specific organic matrix and theintended end application. For most conventional organic resins, aloading of about 35-65 wt.% activated crystalline molecular sieve ispreferred. More preferably, the loading is about 40-60 wt.%.

The molecular sieves useful as the single and/or twinned crystalmolecular sieves in the invention are preferably zeolites. Mostpreferably, the molecular sieves are selected from the group consistingof zeolite A (including varieties and modifications thereof such aszeolite 3A), zeolite X (including varieties and modifications thereofsuch as zeolite 13X), and mixtures thereof. While zeolites A and X havebeen used in desiccant/adsorbent applications previously, the A and Xpowders used for such purposes were polycrystalline in nature and havewetting test values in excess of 9. If desired, minor amounts ofamorphous molecular sieves and/or polycrystalline molecular sieveshaving wetting test values outside the desired range may also beemployed as an admixture. Preferably, such amorphous and/orpolycrystalline molecular sieves represent less than 50 wt.% of thetotal molecular sieve component, more preferably less than 25 wt.%, mostpreferably less than 10 wt. %. Where zeolite 3A is used, preferably ithas a high potassium content as described in U.S. patent applicationSer. No. 08/451,629, now U.S. Pat. No. 5,773,380, filed on the same dateas this case.

The organic matrix component preferably contains an organic resin usefulin desiccant/organic matrix composite applications. Examples of suitablematrix resins are described in U.S. Pat. Nos. 5,177,916 and 5,255,481.The invention is especially useful where the organic matrix contains athermoplastic resin such as a hot melt adhesive. Preferred thermoplasticresins have a Brookfield viscosity (@ 190° C. --ASTM D 3236) of about2000-6000 cP (2.0-6.0 Pa-sec), more preferably about 3000-4000 cP. Analternate characteristic of preferable resins is that they have aviscosity at 124° C. of about 4000-8000 cP. Further alternativecharacteristics of preferable resins are that they have a melt flowindex of about 100-200 and a softening point of at least 90° C. Apreferred classes of resins are olefin copolymers and terpolymers suchas described in U.S. patent application Ser. No. 304,312, now abandonedfiled on Sep. 13, 1994 the disclosure of which is incorporated herein byreference.

The organic matrix component may contain other additives such astackifiers, antioxidants, coloring agents, etc. depending on theintended end use. The amount of tackifier use is preferably about 0-20wt. % based on the total weight of the organic matrix component, morepreferably about 5-15 wt. %. Polyisobutylene is a preferred tackifier.Depending on the particular end use, components other than the molecularsieve component and the organic matrix component may be present in thecomposition, however, preferably the compositions of the inventionconsist essentially of the molecular sieve component and the organicmatrix component.

As noted above, most commercially available molecular sieves marketedfor desiccant/adsorbent applications are predominantly polycrystallinein character such that they have a wetting test value of 9 or more.

The zeolite molecular sieves especially useful in the inventioncompositions (i.e. with wet test values <8.5) can be prepared underspecific manufacturing conditions corresponding to those used to makecertain detergent zeolites such as can be found in U.S. Pat. No.4,371,510 or British Patent Specification 1,563,467. Where a 3A zeoliteis desired, an NaA zeolite prepared in the manner described is simplyexchanged with potassium using a conventional ion exchange techniquesuch as disclosed in U.S. Pat. No. 2,882,243.

The compositions of the invention may be formed by any conventionalblending method. Preferably, the ingredients of the organic matrix arecombined together before addition of the adsorbent component. Where theorganic resin used possesses thermoplastic or hot melt characteristics,the mixing is preferably conducted with heating (e.g., about 180°-310°F.) to reduce the viscosity of the organic resin. The single crystaladsorbent component is preferably thermally activated using conditionsknown in the art before it is combined with the organic matrix. Wheremultiple adsorbents are used, preferably the adsorbents are physicallyblended with each other before addition to the heated matrix.

Once the composition is formed, it can be applied to the desiredsubstrate by any conventional technique.

The aspects of invention are further illustrated by the followingexamples.

EXAMPLE 1

Zeolite 3A particles were prepared in accordance with the abovementioned patents which had a wet test value of 8.0 (Sample A). Forcomparison, two other 3A zeolites were prepared by techniques commonlyused to make desiccant zeolites (i.e. method described in U.S. Pat. No.2,882,243) to have wet test values of 9.3 (Sample B) and 10.1 (SampleC).

EXAMPLE 2

The zeolite 3A samples prepared in Example 1 were each separatelycompounded with an organic matrix comprising 90 wt. %ethylene/propylene/butene terpolymer (Eastman EASTOFLEX T1035) and 10wt. % polyisobutylene tackifier to form 5 gallon samples at 40-60 wt. %zeolite loading using a Brabender mixer. The viscosity of the resultingcompositions was measured at 124° C. and 800 sec⁻¹ shear rate. Theresults plotted in FIG. 1 clearly indicate that the single crystallinematerial (Sample A) exhibits significantly less viscosity than thepolycrystalline zeolites at equivalent loading.

What is claimed is:
 1. A composition comprising a particulate molecularsieve component in a thermoplastic organic resin matrix wherein at least50% weight percent of said molecular sieve component comprises zeoliteparticles in the form of single crystals.
 2. The composition of claim 1wherein said composition contains 35-65 wt. % of said molecular sievecomponent.
 3. The composition of claim 2 wherein said compositioncontains 40-60 wt. % of said molecular sieve component.
 4. Thecomposition of claim 3 wherein said single crystal molecular sieveparticles are zeolites selected from the group consisting of zeolite A,zeolite X and mixtures thereof.
 5. The composition of claim 2 wherein atleast 50 wt. % of the molecular sieve component consists of zeoliteparticles having a wetting test value of 8 or less.
 6. The compositionof claim 1 wherein said organic matrix is an adhesive material.
 7. Thecomposition of claim 6 wherein said organic matrix contains a hot meltadhesive.
 8. The composition of claim 1 wherein said single crystalzeolites include zeolites selected from the group consisting of zeoliteA, zeolite X and mixtures thereof.
 9. The composition of claim 1 whereinsaid resin has a Brookfield viscosity at 190° C. of about 2000-6000 cP.10. A thermoplastic desiccating hot melt adhesive composition comprisingzeolite particles in a thermoplastic organic adhesive matrix wherein atleast 50 weight percent of said zeolite particles are single crystals.11. The composition of claim 10 wherein said composition contains 35-65wt. % of said zeolite particles.
 12. The composition of claim 10 whereinsaid organic adhesive has a Brookfield viscosity @ 190° C. of about3000-4000 cP.
 13. In a window frame spacer comprising a desiccatingadhesive composition of zeolite particles in an organic matrix adheredto a member, the improvement comprising at least 50 weight percent ofsaid zeolite particles being in the form of single crystals.
 14. Thespacer of claim 13 wherein the improvement further comprisessubstantially all of said zeolite particles having a wetting test valueof 8.5 or less.
 15. The spacer of claim 13 wherein said adhesivecomposition is a hot melt adhesive.